Many different types of electronic equipment utilize Liquid Crystal Displays (LCDs) for displaying information to allow a human operator to interface with such equipment. While the exact construction of such LCDs differs depending on their particular application, virtually all comprise a volume of liquid crystal material which, when subjected to an electrical field, changes its axis of polarization. A pair of polarizers are placed on opposite sides of the liquid crystal material so that the polarizers have their axes of polarization orthogonal to each other. In the absence of an electrical field, light passes through the first polarizer and then into the liquid crystal material which is arranged to change the axis of polarization of the light passing therethrough by 90.degree.. The light beams are thus polarized by the liquid crystal material the same as the second polarizer so as to pass through it unimpeded.
However, when an electrical field is applied to the liquid crystal material, the material changes its axis of polarization. Thus, the light passing through the liquid crystal material is no longer polarized 90.degree. so as to be aligned with the axis of the second polarizer. Instead, the light exiting the liquid crystal material is now polarized orthogonal to the axis of polarization of the second polarizer and is thus blocked thereby. By selectively confining the electrical field applied to the liquid crystal material, the amount of light that actually passes through the LCD can be controlled so that certain regions pass light while others do not. In this way, the LCD can be made to display an alphanumeric character or the like.
To improve the contrast of the information displayed by an LCD, backlighting is commonly used. Such backlighting is accomplished by placing a light source, e.g., a fluorescent lamp, behind the LCD (so that the lamp is adjacent to the LCD side opposite the side viewed by an operator). A reflector, typically a parabolic mirror, is placed behind the lamp to reflect and collimate the rays from the lamp, thereby yielding a collimated beam which is directed through the LCD. When fabricating the above-described backlit LCD, there is invariably a trade-off between the degree to which the display can be made small and the degree of sharp contrast obtained by increasing the curvature of the reflector placed behind the light source so as to increase the collimation of the beam directed through the LCD. Increasing the degree of curvature of the reflector increases the degree of collimation of the light reflected thereby, which is desirable, but at the expense of increasing the overall size of the display.
Thus, there is a need for a technique for backlighting an LCD display which allows the LCD to be made small and flat without diminishing the display contrast.